50 BULLETIN OF THE 



the Ophiurans have no iuterambulacrals (adambulacrals). In my paper 

 on Amphiura the laterals were regarded as adambnlacrals, following 

 Ludwig and P. Herbert Carpenter. I am not, however, sure that they 

 are not rather the marginals, and that Agassiz is right in considering 

 that there are no interambulacrals in Ophiurans. The early form and 

 growth of the marginals on the border of the arm in both Asterias and 

 Amphiura is similar. The interambulacrals in starfishes (x\sterias) never 

 approach in form the laterals of Amphiura. In genera allied to the 

 Ophiurans, Astropecten, etc., the marginal plates get ophiuroid in na- 

 ture, and resemble the lateral plates of the young Amphiura. In certain 

 deep-sea genera of starfishes there is a resemblance between the mar- 

 ginal plates and the lateral plates of some Ophiurans when dorsals are 

 not developed. In the light of these facts I must register my doubt 

 whether I am right in following those who regard the lateral plates of 

 Amphiura as adambulacral, homologous with the interambulacral (adam- 

 bulacral) of the starfish. It looks as if true adambulacrals were yet to 

 be made out in Amphiura. The resemblance of the marginal plates of 

 the young starfish to the marginal plates of Zoroaster is still another 

 embryonic feature of deep-water Asteroids. 



The following summary may be made of the preceding obser- 

 vations : — 



1. The first plates to originate in the young starfish are the termi- 

 nals. These plates are simple (not formed by a coalescence of more 

 than one calcification). They form a protecting cap, shielding the 

 newly formed ambulacrals, interambulacrals, and possibly margirials. 



2. The genitals originate after the terminals. The genital which 

 lies contiguous to the madreporic opening does not always antedate in 

 time or excel in size other genitals. It grows around the madreporic 

 body, or end of the madreporic tube. 



3. The madreporic body, madreporite, is a late formation (after the 

 rudiments of the stone canal), 



4. The dorsocentral originates after the terminals and genitals, hefore 

 any plates on the actinal hemisome. 



5. The first plates to form in the body after the genitals have a 

 radial position in a circle inside the genitals. The second circle is also 

 radial, and lies inside the circle of the first body, or somatic radials. A 

 third and inner circle appears before the interradial somatic plate. 



6. The first plate in the circle outside that of the genitals is the 

 first dorsal of the arms. This plate (" Radial," Sladen), when the 



